Research interest in psychiatric and psychosocial aspects of diabetes care has grown exponentially since . Epidemiologic data have accumulated to consistently demonstrate elevations in the prevalence of several psychiatric disorders, as well as subclinical elevations in emotional distress, among individuals living with diabetes. The literature is most developed for depression, where studies indicate between 1.2 and 1.6 times higher prevalence of major depressive disorder among adults diagnosed with type 2 diabetes compared to those without diabetes. Data suggest a bidirectional relationship: depression symptoms predict the onset of type 2 diabetes, and the diagnosis of type 2 diabetes is associated with increased depressive symptoms over time, with the first directional effect appearing to be more robust than the second. Evidence is less supportive of higher prevalence of depression in adults and youth with type 1 diabetes. Risk for depression is related to severity of illness, functional limitations, comorbidity, and treatment burden. Although relatively fewer studies are available, prevalence of anxiety disorders is also between 1.1 and 1.4 times greater among adults with diabetes. Eating disorders appear to be between 1.9 and 3.1 times more prevalent among adolescent females with type 1 diabetes than those without diabetes, although few studies are available. Serious mental illness (i.e., Schizophrenia) is associated with between 1.5 and 2.5 times increased risk for development of type 2 diabetes, most likely through exposure to psychotropic medications and shared environmental and behavioral risk factors. The presence of psychiatric comorbidity, especially depression, which is often comorbid with other psychiatric conditions, has been consistently associated with medication non adherence, sub-optimal glycemic control, and development of diabetes-related complications. The mechanisms to explain these relationships remain poorly understood. Depression, anxiety, and eating disorders could affect health outcomes through biologic (e.g., hypothalamic-pituitary-adrenal axis dysregulation) and/or behavioral (e.g., treatment nonadherence) pathways. However, confounding is possible due to overlap with symptoms of diabetes and comorbid illness, along with shared relationships with socioeconomic and other background variables that may also explain noncausal association. Emotional distress that does not reach thresholds for a psychiatric diagnosis also appears to be quite common in individuals living with diabetes. These psychosocial issues are more prevalent than true psychiatric conditions and are often more closely related to diabetes-related stressors and outcomes. Longitudinal and intervention studies, mostly focused on depression, do not generally support the expectation that improvement in psychiatric conditions or emotional distress would reliably lead to better glycemic control. However, too few high-quality studies are available for this evidence to be conclusive. To have the strongest impact on advancing this field and guiding decisions about patient care, future studies need to be more rigorous in differentiating among psychiatric conditions, elevations in levels of emotional distress, and psychosocial difficulties specific to the burdens of diabetes and its treatment. These studies should also directly evaluate explanatory mechanisms that link these constructs to diabetes health outcomes. Comprehensive approaches to patient-centered care are needed to better understand how to maximize the benefits of intensive treatment for both psychosocial and health outcomes of diabetes care.